Wafer cleaning apparatus

ABSTRACT

An apparatus for cleaning a wafer oriented vertically is provided. The apparatus includes a first brush and a second brush located horizontally from the first brush. During use, a wafer is orientated vertically between the first and second brushes. The brushes are brought into contact with the wafer and rotated thereby engaging the wafer with rollers. By rotating the rollers, the wafer is also rotated. Liquid is sprayed towards the brushes and wafer. By orienting the wafer vertically, liquid and particulates contained therein readily fall from the wafer due to gravity. This is particularly advantageous when cleaning larger diameter wafers in which particulates must be removed from a larger wafer surface area.

FIELD OF THE INVENTION

The present invention relates generally to semiconductor processing andmore particularly to an apparatus for cleaning wafers.

BACKGROUND OF THE INVENTION

Semiconductor manufacturing processes demand wafers, typically siliconwafers, which are substantially particulate free. As the semiconductorindustry moves towards processing larger diameter wafers, for example12-inch diameter wafers, it becomes increasingly difficult to removeparticulates from the wafers. In particular, wafer cleaning processesmust effectively remove particulates from the larger wafer surface areaassociated with the larger diameter wafers. Further, wafer cleaningprocesses must clean the wafers without exerting undue force on thewafers since larger diameter wafers have less mechanical strength thansmaller diameter wafers.

SUMMARY OF THE INVENTION

In accordance with the present invention, an apparatus for cleaning awafer oriented vertically is provided. In one embodiment, the apparatusincludes a first brush and a second brush located horizontally from thefirst brush. The first brush and the second brush define a regionbetween the brushes. Located vertically below the region defined by thefirst and second brushes, is a pair of rollers. During use, a wafer islocated vertically in the region between the first and second brushesand rests on the pair of rollers.

The apparatus further includes first and second brush positioners whichmove the first and second brushes, respectively, from first positions tosecond positions. In this manner, a wafer can be loaded and the firstand second brushes can be moved to contact surfaces of the wafer.

The first and second brushes are mounted on first ends of first andsecond shafts. Motors are connected to pulleys on the second ends of thefirst and second shafts. During use, the motors rotate the first andsecond shafts in opposite directions thereby rotating the first andsecond brushes in opposite directions. This forces the wafer intoV-grooves in the pair of rollers. The wafer is then rotated by rotatingthe pair of rollers.

Preferably, the first and second shafts have central cavities formedtherein and also have perforations in the regions where the first andsecond brushes are mounted. In this manner, liquid can be delivered tothe first and second brushes through the first and second shafts toflush the first and second brushes from the inside out.

The wafer cleaning apparatus can further include first and second setsof spray nozzles capable of spraying a first liquid towards the waferbetween the first and second brushes. The wafer cleaning apparatus canfurther include third and fourth sets of spray nozzles capable ofspraying a second liquid towards the wafer between the first and secondbrushes. In one embodiment, the first liquid and the second liquid arethe same liquid, and the liquid is a surfactant.

Alternatively, the first and second sets of spray nozzles can comprisefirst nozzles capable of spraying the first liquid and second nozzlescapable of spraying the second liquid.

The combination of the scrubbing action on the wafer surfaces by thefirst and second brushes along with the liquid sprayed on the wafersurfaces from the first and second sets of spray nozzles removeparticulates from the wafer surfaces. Since the wafer is orientedvertically, removal of particulates is enhanced since the liquid sprayedon to the wafer surfaces and the particulates trapped therein have atendency to fall from the wafer surfaces due to gravity. This isparticularly advantageous when cleaning larger diameter wafers, such as8-inch or 12-inch diameter wafers, in which particulates must be removedfrom a larger surface area.

Further, by orienting the wafer vertically and by scrubbing both wafersurfaces simultaneously, mechanical stress on the wafer is minimized.This is particularly advantageous for larger diameter wafers which haveless mechanical strength than smaller diameter wafers.

These and other objects, features and advantages of the presentinvention will be more readily apparent from the detailed description ofthe preferred embodiments set forth below taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of wafer cleaning system including a pairof wafer cleaners in accordance with the present invention.

FIG. 2 is a partial top view of one of the wafer cleaners.

FIG. 3 is a partial frontal view of the wafer cleaner.

FIG. 4 is a partial perspective view of the wafer cleaner.

FIG. 5 is a partial side view of the wafer cleaner.

FIG. 6 is a frontal view of wafer cleaner during use in accordance withthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In accordance with the present invention, an apparatus for cleaning awafer oriented vertically is provided. Several elements shown in thefollowing figures are substantially similar. Therefore, similarreference numbers are used to represent similar elements.

FIG. 1 is a perspective view of wafer cleaning system 8 including wafercleaners 14, 16 in accordance with the present invention. Wafer cleaningsystem 8 includes a robotic arm 10, a wet buffer unit 12, wafer cleaners14, 16, a spin drying unit 18, and a finish cassette 20.

Robotic arm 10 has an end-effector 11 which uses a vacuum to hold awafer. End-effector 11 can be rotated from the horizontal position inwhich arm 11A is located horizontally from arm 11B, as shown in FIG. 1,to a vertical position in which arm 11A is located above arm 11B. Wetbuffer unit 12 includes a plurality of horizontal slots in which to holdwafers. Typically, wet buffer unit 12 has sprayers which spray liquid onthe wafers to keep the wafers wet from previous wafer processing, suchas wafer polishing. Wafer cleaners 14 and 16, which are described indetail below, are substantially identical with the exception, in thisembodiment, that a different scrubbing solution is used in wafer cleaner14 than in wafer cleaner 16. Spin drying unit 18 drys the wafer byspinning the wafer at high speeds, thereby removing any liquid from thesurface of the wafer. Spin drying unit 18 is further described inapplication Ser. No. 08/680,739 now Pat. No. 5,778,554 issued on Jul.14, 1998, herein incorporated by reference in its entirety. Finishcassette 20 has a plurality of slots for holding the finished wafers.

During use, robotic arm 10 removes a wafer which is orientedhorizontally from wet buffer unit 12 (the perimeter 22 of the wafer asit is removed from wet buffer unit 12 is indicated in FIG. 1). Roboticarm 10 then rotates the wafer 90° to a vertical orientation and insertsthe wafer into vertical slot 24 of wafer cleaner 14. After processing ofthe wafer in wafer cleaner 14 (described below), robotic arm 10 removesthe wafer from wafer cleaner 14 through slot 24. This sequence isrepeated with wafer cleaner 16. The wafer is then rotated 90° by roboticarm 10. The wafer is then loaded horizontally into spin dryer 18 andfinally is loaded from spin dryer 18 to finish cassette 20.

FIG. 2 is a partial top view of wafer cleaner 14 in accordance with thepresent invention. As shown, wafer cleaner 14 includes a housing 23which includes slot 24 through which a wafer is inserted into wafercleaner 14. Slot 24 is fitted with a door 27 which opens and closes slot24. Wafer cleaner 14 further includes a first rotary brush 26 and asecond rotary brush 28. Brushes 26, 28 are made of polyvinyl alcohol(PVA) foam although other materials such as nylon, mohair or a mandrelwrapped with polishing pad material can be used. In one embodiment,brushes 26, 28 are PVA foam manufactured by KANEBO of Japan. Brushes 26,28 are located horizontally from one another.

Located between brushes 26, 28, and defined by brushes 26, 28, is aregion 30. Located vertically below region 30 is a first roller 32 and asecond roller 34. Rollers 32, 34 have V-grooves 36, 38, respectively,extending around the periphery of the rollers.

Brushes 26, 28 are mounted to first ends of shafts 40, 42, respectively.Rotary unions 41, 43 are mounted to second ends of shafts 40, 42,respectively. Shafts 40, 42 have central cavities formed therein whichallow liquid to flow from rotary unions 41, 43 through shafts 40, 42,respectively. Further, shafts 40, 42 have perforations in the regions ofshafts 40, 42 to which brushes 26, 28, respectively, are mounted. Theperforations allow liquid to be distributed from shafts 40, 42 tobrushes 26, 28.

Wafer cleaner 14 further includes a plurality of spray nozzles. Inparticular, located proximate to and above brush 26 is a first set ofspray nozzles 56. Similarly, located proximate to and above brush 28 isa second set of spray nozzles 58. During use, first and second sets ofspray nozzles 56, 58, spray liquid towards a wafer located betweenbrushes 26, 28, respectively. In one embodiment, first and second setsof spray nozzles 56, 58, each comprise three individual spray nozzles.

Servo motors 44, 46 are connected to pulleys on the second ends ofshafts 40, 42 by drive belts 45, 47, respectively. Shaft 40 is mountedinto bearings 48 and 50. Similarly, shaft 42 is mounted into bearings 52and 54.

FIG. 3 is a partial front view of wafer cleaner 14 in accordance withthe present invention. As shown in FIG. 3, bearings 52, 54 are mountedto an upper movable plate 80. Bearings 48, 50 are mounted to a lowermovable plate 82. Motors 46, 44 are also mounted to movable plates 80,82, respectfully. During use, motors 44, 46 rotate shafts 40, 42 inopposite directions, thereby rotating brushes 26, 28 in oppositedirections, respectively. Generally, brushes 26, 28 are rotated between50 to 1500 revolutions per minute.

Further, upper plate 80 is coupled to a first end 84A of a pivot 84 andlower plate 82 is coupled to a second end 84B of pivot 84. Pivot 84 iscoupled at its center 84C to a section 23A of housing 23 (oralternatively to a plate 23A connected to housing 23). Also coupled tosection 23A is an air cylinder 86. Air cylinder 86 has a piston 88coupled by a pressure transducer 89 to upper plate 80.

By controlling pressurized air flow into and out of air cylinder 86, theposition of piston 88 can be controlled, and hence the position ofbrushes 26, 28 can be controlled. In particular, when piston 88 ispartially extended as in FIG. 3, brushes 26, 28 are located at adistance from one another. However, when piston 88 is retracted into aircylinder 86 (moved in the direction towards section 23A as indicated bythe arrow in FIG. 3), upper plate 80 is also moved towards section 23A.Since shaft 42 is mounted to upper plate 80, shaft 42 and brush 28 arealso moved towards section 23A.

The movement of upper plate 80 towards section 23A causes first end 84Aof pivot 84 to also move towards section 23A. Since pivot 84 is coupledat its center 84C to section 23A, the motion of first end 84A causes anequal and opposite motion of second end 84B of pivot 84. Thus, as upperplate 80 moves towards section 23A, lower plate 82 moves away fromsection 23A. Since shaft 40 is mounted to lower plate 82, shaft 40 andbrush 26 are also moved away from section 23A. The net result is thatwhen piston 88 is retracted, brushes 26, 28 are moved towards oneanother and when piston 88 is extended (moved away from section 23A),brushes 26, 28 are moved away from one another. Further, the pivot 84ensures that the perpendicular component of force (further describedbelow) of each brush (26, 28) is equal and opposite to that of the otherbrush (28, 26).

FIG. 4 is a partial perspective view of wafer cleaner 14 in accordancewith the present invention. As shown in FIG. 4, mounted to upper plate80 are bearings 90, 92 and 94. Running through bearings 90, 92 is afirst immobilized shaft and running through bearing 94 is a secondimmobilized shaft (these shafts are not illustrated in FIG. 4 forpurposes of clarity). As piston 88 of air cylinder 86 is extended andretracted and upper plate 80 moved, upper plate 80 slides along theshafts running through bearings 90, 92, and 94. In this manner, plate 80is prevented from moving in any direction except perpendicular to theplane of section 23A. Similar bearings and shafts are mounted to plate82 which also prevent plate 82 from moving in any direction exceptperpendicular to the plane of section 23A.

FIG. 5 is a partial side view of wafer cleaner 14 in accordance with thepresent invention. As shown in FIG. 4, a drive belt 60 couples rollers32, 34 to roller motor 62. An idler pulley 61 maintains a proper tensionin drive belt 60. During use, motor 62 causes drive belt 60 to movethereby rotating rollers 32, 34. Also shown in FIG. 5 are shafts 96 and98 which run through bearings 90, 92 and 94, respectively.

FIG. 6 is a partial frontal view of wafer cleaner 14 during use inaccordance with the present invention. As shown in FIG. 6, initiallybrushes 26, 28 are at positions 66, 68, respectively (indicated bydashed circles). Wafer 64 is then inserted vertically through slot 24into region 30 by robotic arm 10 (not shown). While the wafer is held byend-effector 11 (not shown), brushes 26, 28 are moved towards each otherto positions 70, 72, respectively. Typically, brushes 26, 28 travelapproximately 0.5 inches between positions 66 and 70, 68 and 72,respectively. At positions 70, 72, brushes 26, 28 contact first andsecond surfaces 74, 76, respectively, of wafer 64. The perpendicularcomponent of force (force exerted perpendicular to planes formed bysurfaces 74, 76 of wafer 64) exerted by brush 26 (and brush 28) on towafer 64 is measured and controlled. For example, by measured andcontrolling the force exerted by piston 88 on pressure transducer 89(FIG. 3), the perpendicular component of force exerted by brushes 26, 28on to wafer 64 is measured and controlled. Generally, the perpendicularcomponent of force exerted by each brush on wafer 64 is less than 50pounds per square inch (PSI) and preferably is 5 PSI.

End-effector 11 then releases wafer 64, robotic arm 10 removesend-effector 11 from wafer cleaner 14 and door 27 over slot 24 isclosed. As best seen in FIG. 5, wafer 64 is held by brushes 26, 28 at afirst position 64A. Brushes 26, 28 are then caused to rotate by servomotors 44, 46 (FIGS. 2, 3), respectively. Servo motors 44, 46 rotatebrushes 26, 28 at substantially the same speed. As shown in FIG. 6,brush 26 is rotated clockwise and brush 28 is rotated counterclockwise.This rotation of brushes 26, 28, forces wafer 64 (to a position 64B inFIG. 5) into V-grooves 36, 38 of rollers 32, 34, respectively. Thisengages wafer 64 to rollers 32, 34. Motor 62 then causes rollers 32, 34to rotate which, in turn, cause wafer 64 to rotate. Generally, the waferis rotated at less than 500 RPMs.

Referring back to FIG. 6, brushes 26, 28 are then flushed from theinside out by liquid supplied to brushes 26, 28 from shafts 40, 42.Substantially simultaneously, first and second sets of spray nozzles 56,58, spray liquid on brush 26, first surface 74 of disk 64 and brush 28,second surface 76 of disk 64, respectively.

In one embodiment, wafer cleaner 14 further includes third and fourthsets of spray nozzles 57, 59 located below first and second sets ofspray nozzles 56, 58, respectively. During a first stage of the wafercleaning cycle, a first liquid is sprayed from sets of spray nozzles 57,59 (or 56, 58). During a second stage of the wafer cleaning cycle, asecond liquid is sprayed from sets of spray nozzles 56, 58 (or 57, 59).For example, the first liquid can be a surfactant and the second liquidcan be de-ionized water. Alternatively, the same liquid can be sprayedfrom sets of spray nozzles 56, 57, 58, 59 simultaneously. Further,additional liquids can be sprayed during various stages of the wafercleaning cycle by adding additional sets of spray nozzles.

Alternatively, only first and second sets of spray nozzles 56, 58 areused, but individual nozzles of each of the sets of spray nozzles areplumbed to different liquids. In this manner, selective nozzles canspray different liquids at various stages in the wafer cleaning cycle.

The flow of liquid to brushes 26, 28 and first and second sets of spraynozzles 56, 58 is controlled by opening and closing valves coupled tofeed lines (not shown) which are plumbed to shafts 40, 42 via rotaryunions 41, 43, respectively and sets of spray nozzles 56, 58. Further,the operation of wafer cleaner 14 is controlled by a conventionalprogrammable logic controller (PLC), for example by a PLC model #2600manufactured by Control Technology Corp. located in Hopkinton, Mass.

The combination of the scrubbing action on the surfaces 74, 76 of wafer64 caused by the rotation of brushes 26, 28 along with liquid suppliedthrough brushes 26, 28 and by sets of spray nozzles 56, 58, removesparticulates from surfaces 74, 76 of wafer 64. In particular,particulates are scrubbed from surfaces 74, 76 by brushes 26, 28,respectively. These particulates are flushed from brushes 26, 28 by theliquid supplied to brushes 26, 28 through shafts 40, 42.

Further, particulates which are loosened by the scrubbing action ofbrushes 26, 28, but remain on surfaces 74, 76 of wafer 64, are flushedfrom surfaces 74, 76 by liquid sprayed from sets of spray nozzles 56,58. By orienting wafer 64 vertically instead of horizontally, theremoval of particulates from the surfaces 74, 76 is enhanced. Inparticular, by orienting wafer 64 vertically, liquid sprayed on tosurfaces 74, 76 of wafer 64 and particulates trapped in the liquid havea tendency to fall from surfaces 74, 76 due to gravity. In contrast, ifwafer 64 were oriented horizontally, particulates would tend to be movedaround on surfaces 74, 76 and would not be as readily removed. Thus,wafer cleaner 14 is particularly well suited for larger diameter wafersin which particulates must be removed from a larger surface area. Forexample, wafer cleaner 14 is particularly well suited for cleaning8-inch and 12-inch diameter wafers.

Further, by orienting wafer 64 vertically and by scrubbing both surfaces74, 76 simultaneously, mechanical stress on wafer 64 is minimized. Thisis because the perpendicular component of the force exerted by brush 26on wafer 64 is offset by the perpendicular component of the forceexerted by brush 28 on wafer 64. (The perpendicular components of forceexerted by each brush of the wafer is equal and opposite to that of theother brush.) Thus, the net force which is exerted on wafer 64 bybrushes 26, 28 is substantially parallel to the plane formed by surface74 (or surface 76). Since wafer 64 has the greatest mechanical strengthin this plane, wafer cleaner 14 is well suited for larger diameterdisks. (Larger diameter disks generally flex when force is exerted in aplane perpendicular to side 74.)

After wafer 64 has been scrubbed for a predetermined period of time,generally 30 to 120 seconds and typically 45 seconds, the flow of liquidto brushes 26, 28 and sets of spray nozzles 56, 58, is shut off.Substantially simultaneously, the rotation of rollers 32, 34 and brushes26, 28 is stopped. Door 27 over slot 24 is opened, robotic arm 10inserts end-effector 11 into slot 24 and the end-effector 11 engageswafer 64. Then, Brushes 26, 28 are moved back to positions 66, 68,respectively, and robotic arm 10 removes wafer 64. Wafer cleaner 14 isnow ready to process another wafer.

Referring to FIG. 1, by using two wafer cleaners 14, 16, sequentially, awafer can be scrubbed and rinsed with two different solutions. In oneembodiment, for example, the scrubbing liquid in wafers cleaner 14 is anammonia solution or a surfactant available from Valtec or Allied. Thescrubbing liquid in wafer cleaner 16 is de-ionized water. Thisarrangement is particularly advantageous since surfactant residue on thewafer from wafer cleaner 14 is readily removed by the water rinse inwafer cleaner 16. However in alternative embodiments, other scrubbingliquids are used, for example acid or caustic solutions are used ineither wafer cleaner 14 or 16. Further, it is understood that only asingle wafer cleaner can be used, or that several wafer cleaners can beused.

Although the present invention has been described with reference topreferred embodiments, persons skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention. For example, the wafer can be a generallycircular silicon wafer, glass wafer, ceramic wafer, oxide wafer,tungsten wafer although other types of wafers can be used. Further,although various values have been provided, it is understand that thecycle time, rotational speed of the brushes, rotational speed of thewafer and perpendicular component of force exerted by the brushes of thewafer, depend upon the particular application. Thus, the invention islimited only by the following claims.

We claim:
 1. A wafer cleaning apparatus comprising:a first brush; asecond brush located horizontally from said first brush, said firstbrush and said second brush defining a region in between; a pair ofrollers located vertically below said region defined by said first brushand said second brush; a first brush positioner which moves said firstbrush from a first position to a second position, wherein said firstbrush positioner comprises a first plate, said first brush mounted to afirst shaft mounted to said first plates; and a second brush positionerwhich moves said second brush from a first position to a secondposition, a distance between said first brush and said second brushbeing greater when said first brush is in said first position and saidsecond brush is in said first position than when said first brush is insaid second position and said second brush is in said second position,wherein said second brush positioner comprises a second plate, saidsecond brush mounted to a second shaft mounted to said second plate,said first plate being coupled to said second plate by a pivot.
 2. Thewafer cleaning apparatus of claim 1 further comprising an air cylinderhaving a piston, said piston coupled to said first plate and adapted tomove said first plate and by said pivot adapted to move said secondplate.
 3. The wafer cleaning apparatus of claim 2 further comprising apressure transducer, said piston being coupled to said first plate bysaid pressure transducer.
 4. The wafer cleaning apparatus of claim 3wherein said first brush and said second brush contact a wafer when insaid second position, a perpendicular component of force exerted on saidwafer by said first brush and said second brush being controlled bymeasuring and controlling the force exerted by said piston on saidpressure transducer.
 5. A wafer cleaning apparatus comprising:a firstbrush; a second brush located horizontally from said first brush, saidfirst brush and said second brush defining a region in between; a pairof rollers located vertically below said region defined by said firstbrush and said second brush; a housing having a vertical slot therein;and a door which opens and closes said vertical slot.
 6. The wafercleaning apparatus of claim 5 wherein each roller of said pair ofrollers has a V-groove therein.
 7. The wafer cleaning apparatus of claim5 further comprising:a first shaft having said first brush mountedthereon; and a second shaft having said second brush mounted thereon. 8.The wafer cleaning apparatus of claim 7 further comprising:a firstrotary union mounted to said first shaft; and a second rotary unionmounted to said second shaft.
 9. The wafer cleaning apparatus of claim 7further comprising:a first motor connected to said first shaft capableof rotating said first shaft and thereby rotating said first brush; anda second motor connected to said second shaft capable of rotating saidsecond shaft and thereby rotating said second brush.
 10. The wafercleaning apparatus of claim 5 wherein said first brush and said secondbrush are made from the group consisting of polyvinyl alcohol (PVA),nylon, mohair and polishing pad material mounted on a mandrel.
 11. Thewafer cleaning apparatus of claim 5 further comprising a motor coupledto said pair of rollers capable of rotating said pair of rollers.
 12. Awafer cleaning apparatus comprising:a first brush; a second brushlocated horizontally from said first brush, said first brush and saidsecond brush defining a region in between; a pair of rollers locatedvertically below said region defined by said first brush and said secondbrush; a first shaft having a first end with said first brush mountedthereon; and a second shaft having a first end with said second brushmounted thereon, wherein said first shaft has a cavity formed thereinand has perforations in the region where said first brush is mounted andwherein said second shaft has a cavity formed therein and hasperforations in the region where said second brush is mounted.
 13. Awafer cleaning apparatus comprising:a first brush, a second brushlocated horizontally from said first brush, said first brush and saidsecond brush defining a region in between; a pair of rollers locatedvertically below said region defined by said first brush and said secondbrush; a first set of spray nozzles capable of spraying a first liquidtowards said first brush; a second set of spray nozzles capable ofspraying said first liquid towards said second brush; a third set ofspray nozzles capable of spraying a second liquid towards said firstbrush; and a fourth set of spray nozzles capable of spraying said secondliquid towards said second brush.
 14. The wafer cleaning apparatus ofclaim 13 wherein said first liquid is a surfactant.
 15. A wafer cleaningapparatus comprising:a first brush; a second brush located horizontallyfrom said first brush; a first set of spray nozzles, wherein said firstset of spray nozzles comprises a first nozzle capable of spraying afirst liquid towards said first brush and a second nozzle capable ofspraying a second liquid towards said first brush; and a second set ofspray nozzles, wherein said second set of spray nozzles comprises afirst nozzle capable of spraying said first liquid towards said secondbrush and a second nozzle capable of spraying said second liquid towardssaid second brush, said second liquid being different than said firstliquid.